SYDNEY — A powerful earthquake measuring magnitude 6.8 rocked parts of the South Pacific nation of Papua New Guinea on Wednesday, officials said. There were no immediate reports of casualties or damage.

The U.S. Geological Survey said the earthquake was located 40 miles west-southwest of Panguna in Papua New Guinea. It struck at 8:31 p.m. at a depth of 36 miles, it said.

The Pacific Tsunami Warning Center said a destructive Pacific-wide tsunami was not likely.

An official with Papua New Guinea’s Disaster Management Office said there had been no reports of any damage or injuries, and the quake had not been felt in the capital, Port Moresby.

Earthquakes are common in Papua New Guinea. The country lies on the “Ring of Fire” — an arc of earthquake and volcanic activity that stretches around the Pacific Rim.

A magnitude-7.0 earthquake on the northern coast in 1998 generated a large tsunami that swamped several villages, killing about 2,200 people.

USGS said 22 earthquakes measuring more than magnitude 7.5 have been recorded in the New Guinea region since 1900.